1. Field of the Invention
The invention relates to a fogging detecting system for an automotive vehicle and a method for controlling the system, which is adapted to be able to secure the view of a driver by removing the fog formed on a wind shield glass of the automotive vehicle, more in particular, to a defogging system for an automotive vehicle and a method for controlling the same, which can prevent the excessive loss of power by expecting the time when the fog will occur approximately to the actual condition in consideration of the temperature distribution around the wind shield glass.
2. Background of the Related Art
In general, a fogging phenomenon of forming dewdrops at the wind shield glass is produced when the humidity at the inside of the automotive vehicle is high and exterior temperature is low. In other words, as shown in FIG. 1, fog is produced when the surface temperature Ts of the wind shield glass is lower than the dew point temperature Td determined by the humidity around the wind shield glass, to thereby veil the view of the driver. Accordingly, most of the automotive vehicles are provided with the defogging system for removing the fog by using air discharged through a defrost duct of an air conditioning system at the time of the occurrence of the fog.
The defogging system not only accomplishes the safety of the driver by securing good view of the driver but improves the pleasant atmosphere, by early detecting the occurrence of the fog at the wind shield glass to thereby suppress the occurrence of the fog and remove it early. Accordingly, most of the defogging system detects the occurrence of the fog by using a fog sensor mounted to the wind shield glass, and if the occurrence of the fog is expected, the defogging system is operated to suppress the occurrence of the fog and remove the fog occurred previously.
The fog sensor is comprised of a temperature sensor for detecting the surface temperature of the wind shield glass and a humidity sensor for detecting the humidity around the wind shield glass, and obtains the dew point temperature by using the function of the temperature and the humidity. Accordingly, the accuracy of the fog sensor is determined by how accurately it expects the dew point temperature, and is designed in various shapes to obtain the optimum dew point temperature.
As a result, it is most important to calculate the dew point temperature to expect the occurrence of the fog accurately. However, most of the fog sensors calculate the dew point temperature only on the basis of the surface temperature of the wind shield glass, or only on the basis of the peripheral temperature of the wind shield glass, so that the accuracy of the calculation of the dew point temperature is doubted.
FIG. 9 shows a graph expecting the occurrence of the fog on the basis of the surface temperature of the wind shield glass or the peripheral temperature. In this regard, a deviation between the dew point temperature and the surface temperature of the glass, which varies along with the lapse of time, are shown, after the dew point temperature is calculated on the basis of the surface temperature of the glass or the peripheral temperature of the glass.
As a result of the expectation of the time when the fog is occurred on the basis of the surface temperature of the glass, it is expected that the fog will be occurred at about nine minutes after the start up of the automotive vehicle. However, the fog was actually occurred at twenty seven minutes after the start up of the automotive vehicle, so there was a difference of about eighteen minutes. That is, the defogging system was operated at about eighteen minutes faster than the time actually required, to thereby dissipate the energy.
Further, as a result of the expectation of the time of the fog occurrence on the basis of the peripheral temperature, it is expected that the fog will occur at about seven minutes after the start up of the automotive vehicle. However, the fog was actually occurred at about twenty seven minutes after the start up, to thereby produce a difference of about twenty minutes. That is, the defogging system was operated at about twenty seven minutes faster than the time actually required, to thereby dissipate the energy.
After all, it is an important point to calculate the dew point temperature more accurately to reduce the consumption of the energy. Accordingly, several methods have been devised to calculate the accurate dew point temperature, and the following US patent discloses one of those methods.
With regard to a fog sensor unit disclosed in U.S. Pat. No. 6,422,062B1, it comprises in a protection dome a glass temperature sensor mounted to the wind shield glass, an air temperature sensor for sensing the temperature of the air, which is positioned a predetermined distance apart from the wind shield glass, and a humidity sensor for sensing the humidity of the air, whose temperature is sensed by the air temperature sensor.
The fog sensor unit determines whether there occurs a fog or not by comparing the glass temperature sensed by the glass temperature sensor with the dew point temperature, after confirming the dew point temperature of a position isolated a predetermined distance from the wind shield glass by sensing the temperature and the humidity of the position by using the air temperature sensor and the humidity sensor.
However, the fog sensor unit calculates the dew point temperature by measuring the temperature with the air temperature sensor only, and the glass temperature sensed by the glass temperature sensor is not used in the calculation of the dew point temperature. Accordingly, it is impossible to know the temperature distribution depending on the air conditioning and the state of the vehicle, so that the accuracy and the responsive property were decreased at the time of expecting the occurrence of the fog, when the fluctuation of the temperature is serious due to outer disturbances such as the air fluctuation at the inside of the vehicle, and the like.